97 Effect of psyllium husk supplementation on equine fecal nutrient composition and in vitro fermentation

Ingestion of sand by equids housed in areas with sandy soils can cause serious and potentially life-threatening issues. Feeding psyllium husk (Plantago ovata) is one of the most common treatments used within both the domestic horse and zoological communities for mitigating sand accumulation in the large intestine of hindgut fermenting species. The degree to which the large intestine microbiome adapts to addition of psyllium in the diet, thereby reducing its efficacy, remains unknown. The aim of this study was to identify the degree to which psyllium husk (PSY) degradation changed over a 14-d supplementation period, both in vivo and using an in vitro batch culture system. We hypothesized that the hindgut microbiome would adapt to PSY supplementation over time, altering fermentation patterns. Young Quarter Horse geldings (437 ± 48 kg, 20 ± 1 mo of age; mean ± SD) were randomly assigned to receive either PSY supplementation (n = 6) or no supplementation (control; n = 2) in a repeated measures design. Horses assigned to treatment received PSY mixed into their morning concentrate ration at a rate of 0.31g DM/kg BW on d 1–14. Fecal samples were collected from all horses at the time of the morning feeding on d 0–14. Fecal samples were analyzed for dry matter (DM), neutral detergentfiber (NDF), acid detergent fiber (ADF), and hemicellulose (HEM; calculated as NDF-ADF). Fecal samples collected on d 0, 7, and 14 from horses receiving PSY were used to create fecal inocula representing each individual horse to determine in vitro dry matter degradability (DMD) of PSY when included as a substrate for in vitro fermentation. Gas production was measured repeatedly over a 48-h period, while DMD was measured at 12, 24, and 48 h. Fecal composition data were analyzed as a linear mixed effects model, with main effects and interaction of treatment and day. In vitro gas production and DMD were analyzed with main effects and interaction of day and hour of fermentation. Fecal DM (P = 0.93) and HEM (P = 0.82) were not different on any day of the study. In vitro, gas production was greater (P < 0.05) for inocula created from d 7 and d 14 feces compared with d 0. In vitro DMD was also greater (P < 0.05) at 24 and 48 h on d 7 and 14 compared with d 0. Findings indicate that microbial degradation of PSY may increase as treatment duration is lengthened, which could reduce the potential efficacy of PSY over time.